Biochemistry
Lec: 1 Dr. Ahmed Dalalbashi
"Nutrition"
Nutrition is the science that deals with the relationship of food with the
functioning living organism.
The nutritional requirements of a person are 3 folds:
1. Water.
2. Calories and
3. Specific molecules (Vitamins, minerals and oxygen).
Water
:
Water is more essential to life than is food, for a person may live weeks
without food but only days without water.
It is an essential component of blood, lymph, the secretions of the body
and every cell in the body. More than ½ the adult’s weight is water (60%
for men and 54% for women)..
The extra cellular compartment accounts for 1/3 of body water including
plasma and interstitial spaces, while the intracellular fluid contains 2/3 of
body water.
Fluid is necessary for the functioning of every organ in the body. It is a
structural component of cells, when a cell loses their water they lose their
shape. It is the universal medium in which the various chemical reactions
of the body take place.
As a carrier it aid in digestion, absorption, circulation and excretion. It is
essential in the regulation of body temperature. It plays an important part
in mechanical functions, such as the lubrication of joints and the
movement of the viscera in the abdominal cavity.
Waste products from the tissues are transferred to the blood in a watery
solution, they are carried by the blood which is about 80% water and they
are excreted via the kidneys in urine (about 97% water).
The same water is reused many times and for different purposes.
Approximately 8 L of digestive juice are produced and secreted by the
glands in 24 h.
Over 4L of water are always circulating in the blood stream. It is
estimated that some 50 L of water cross the cell membranes in a day.
In the kidney large volumes of water (180L) carry the dissolved waste
materials through the capsule of the nephrones, most of the water, with
some of its useful dissolved materials is reabsorbed (99%).
The urine, which is excreted, is the concentrated aqueous solution of the
waste products.
Water intake and output:
Normally the body losses water through 4 routes:
1. From the skin.
2. From the lung (Total about 800 ml)
3. From the kidneys (1-1.5L) and
4. From the intestine (about 200 ml). Large amount of water are also
lost in abnormal conditions including; fever, vomiting, burns and
hemorrhage. Fluids are replaced by the ingestion of liquids and
foods containing water.
Although some water is formed within the body as an end product of food
metabolism, from 1-1.5 L of water or other liquids should be consumed
daily in order to insure a sufficient amount of water for body functions.
Caloric requirements:
The caloric requirement of man may be discussed in terms of protein,
lipids, and carbohydrates. These complicated organic substances are
synthesized by the plants from simple inorganic materials such as CO2,
H2O, NH3, SO4 etc.
Animals and human get their energy from the food, which is derived
directly or indirectly from the plants.
Energy taken as food is used for the following purposes:
1. To perform mechanical work.
2. To maintain the tissues.
3. For growth.
Energy Contents of Food:
It is found that 1 g of protein will give approximately 5.4 Kcal. Of heat,
while 1 g of fat will give approximately 9.3 Kcal. And 1 g of
carbohydrate will give approximately 4.1 Kcal and 1 g of ethanol gives
7.1 Kcal of heat.
It is known that a calorie is the amount of heat or energy required to raise
the temperature of 1 g of water 1 °C. Sometimes the joule replaces the
calorie as 1 calorie is equivalent to 4.184 joules.